If the baby is always on its back and cannot be examined during the 4D examination, you can move around and wait until the baby turns around, or you can come back a few days later. The fetus is always in the position of lying on its back, probably because the umbilical cord is short and turning around will make it uncomfortable. However, as long as the blood supply is normal, it will not affect the fetus. At this time, it is recommended that you can move more, mainly by walking, or going up and down stairs, but not too fast, and then go for ultrasound after the activity. If the baby still hasn’t turned over, you can consider coming back for 4D ultrasound in a few days. 4D ultrasound examination is to determine whether the fetus is developing normally through ultrasound. The 4D ultrasound allows you to see the real-time dynamic activities of the fetus in your belly. The best time to have a 4D ultrasound varies from person to person, and the results may vary depending on the needs. In general, the best time to have an ultrasound is between 16 and 24 weeks of pregnancy, when there is more amniotic fluid and it is also suitable for fetal malformation screening. 4D ultrasound can observe the growth and development of the fetus in the womb in many aspects, and has become a necessary examination during pregnancy. Therefore, if the baby is lying on its back during the 4D ultrasound examination, you can move around more, but you should do so according to your ability.